THEORY OF R ESl'lK ATIOfN^ g j[ 



It appears from a number of experiments made by Dr. Hales, The number of 



Dr. ?4enzie''^ and Mr. Davy, that the number of refpi rations [^^P';^||j;;'^'^'^^J* 



made in a given time, as well as the quantity of air taken in different per- 



into the Imwsi are liable to coi)fiderabJe variations in different ^°i.'' (j"*^™ '* '° 

 " 26 J but are 



people. Some have calculated ihe number of refpirations at commonly, about 

 II- only in a irtinute, others at 20; Mr. Davy informs us that*®' 

 he makes 26 or 27 in a minute ; but having frequently endea- 

 voured to count the refpirations made by different people, in a 

 given time, and without their knowledge, I have found them 

 vary from IS to 26 in a minute, moil commonly, hovvever, 20 

 or 21 ; and 21 in a minute make 5o,240 in 2^ hours. ^ 



The quantity of air taken in at each refpiraition, muil be Each refpiratloia 

 in proportion to the fize of the perfon and the capacity of his^^'^.^ fnche^f 

 lungs. About 41 cubic inches of air afe taken in at every na-air. 

 tural infpiration. 



We now come to confider the changes which, are produced. Phenomena of 

 both in the air and blood, by refpiration. 1. On the changes '^^P'"^'°°* 

 effeded in the air. Dr. Prieftley, M. Lavoifier, and Mr. 

 l)avy, have furnilhed us vvith niSny intere(!ing and inflEruf^ive 

 experiments oh thrs fubje6t. The changes are, 1. Tha:t a Some air difap- 

 portion of the air difappears; 2. That the air expired differs P""'. ^'*°"^v - 



\ ' "^ ' r ^ one-nineteenth J 



from that nrft taken into the lungs, in containing carbonic and the expired 

 acid, and water in the Rate of vapour. Dr. Menzies has *^'' ** *^""'*'' 

 ftiewn, that J^th of the ait infpired difappears m the lungs, 

 and the experiments of Lavoifier, which were made with 

 much precifion, differ but little from the above ftatenieht. I 

 never knew the quantity of air which difappears to be lefs 

 than y^^th part of the whole taken into the lungs ; this may 

 however be liable to variation in different people. 



It has hitherto been fuppofed that the portion of air wtich The abforbcd atf 

 difappears, confifts of the oxigen only: Mr. Davy has, how- ^'^^ '^°"sht to 



• r n p r f / , be ojfigen Only J 



ever, given tome very Ifrong realons tor luppofing that part 



of the azote Hkewife difappears during refpiration. He fup- but appears tobei 



pofes that the average quantity of air which is abforbed at "^^*'' ^*^'* 



every refpiration, amounts to \A cubic inches, of which 0.2 



are azot and 1.2 oxigen. 



Lime-water deteds carbonic acid gas irt the air emitted The emitted air 

 from the lungs, and the quantity of this gas may eafily be efti.^^.^'^'"***^^^"^^ 

 mated, by receiving the air expired into a graduated glals 

 jar, ftanding over mercury; a little caullic foda being intro- 

 duced, the abforption which takes place denotes the quantity" 



VoL.XI.—JoNE, 1305. G •£ 



